(1) Field of the Invention
This invention relates to a method for sanitizing a biological tissue to eliminate infectious agents and small proteins such as conformationally altered prions, bacteria, fungi, parasites and viruses, particularly in fresh meat carcasses to provide the highest possible health protection standards to meat consumers.
(2) Description of the Related Art
Transmissible Spongiform Encephalopathies, or Prion diseases, are fatal neurodegenerative diseases that affect both humans and animals. Examples include Creutzfeldt-Jacob disease (CJD) in humans, Bovine Spongiform Encephalopathy (BSE) in cattle and scrapie in sheep and goats. They are characterized by a long incubation period, ranging from months to years, and a variable length clinical course, both determined by the particular infection and the species involved. In Japan, 2 cases of BSE in cattle under the age of 30 months were found and another two (2) cases were found, also under the age of 30 months, in Europe (Dehaven, 2003). BSE is caused by a transmissible agent, which has been detected in the brain, spinal cord of natural cases of BSE and the distal ileum, optic nerve, dorsal root ganglia and in the bone marrow of cattle experimentally infected with BSE. The infectious agent has not been detected in other tissues which have been tested in transmission experiments in laboratories rodents (Wells et al., 1998).
While there has been an overall increase in the number of CJD cases observed, this was attributed to an ascertainment bias; however, a new form of CJD with a different clinical presentation and pathology was identified in 1996 (Will et al. 1996). This led scientists to suspect a possible link between BSE and the new form of the human Creutzfeldt-Jacob disease (vCJD). Experimental strain typing of variant vCJD has shown that the transmissible agent responsible for this disorder is identical to that in BSE, providing further evidence to support the hypothesis that exposure to the BSE agent, presumably through diet, is the cause of vCJD (Ironside, 1998). Since 1995, vCJD has killed more than 150 people in Europe based upon post mortum testing, and it is uncertain as to how many people harbor latent vCJD infections from having eaten tainted beef.
The nature of the transmissible agent in BSE is not known. Currently, the most accepted theory is that a component of the infectious agent is a normal protein (the prion protein) found in nervous tissue of all mammals (Prusiner and Scott, 1997). This prion protein assumes a typical conformation in animals not incubating BSE; however, animals that are incubating the disease have, in addition to the normal form (prion protein cellular, PrPc a conformationally altered form (prion protein scrapie, PrPSc).
Hilton et al., (1998) reported that vCJD can be detected in the human appendix before the first symptoms of the disease appeared. Studies on scrapie, the sheep equivalent of CJD, revealed that lymphoid tissue, such as in the gut, tonsils, and spleen, were infected with prions a third of the way through the incubation period and long before symptoms developed (Schreuder et al., 1998). Cattle incubating BSE without having any clinical signs or detectable pathology of the disease were identified in Ireland (Rogers et al., 2000).
Unlike microbes, conformationally altered prions are not completely destroyed by sterilization, traditional autoclaving, disinfectants, radiation, or cooking and they remain intact for years after an infected animal is buried. They are currently totally degraded only with incineration at temperatures greater than 1,000° F.
Secretary of Agriculture Ann M. Veneman at a press conference on Dec. 30, 2003, announced that the U.S. Dept. of Agriculture will continue its BSE surveillance program, available on the APHIS web site (www.aphis.usda.gov/oa/bse/), and will take the following additional actions to guard against BSE:                Ban of all nonambulatory cattle from the human food chain.        Usage of mechanically separated meat is prohibited in human food.        Specified risk materials skull, brain, trigeminal ganglia, eyes, vertebral column, spinal cord and dorsal root ganglia of cattle over 30 months of age and the small intestine of cattle of all ages cannot be used in the human food supply. These enhancements are consistent with the actions taken by Canada after the discovery of BSE in May, 2003.        Ban the practice of air-injection stunning.        Ante- and post-mortem inspection of cattle that are slaughtered in the United States. As part of the ante-mortem inspection, FSIS personnel look for signs of disease, including signs of central nervous system impairment. Animals showing signs of systemic disease, including those exhibiting signs of neurological impairment, are condemned. Meat from all condemned animals has never been permitted for use as human food.        Specified risk materials cannot be used for Advanced Meat Recovery.        
However, the demonstration of a causal relationship between the agent of BSE and vCJD, the finding that prions can lurk in organs long before people or animals show signs of the disease, the identification of BSE positive animals under the age of 30 months; the unavailability of diagnostic tests that would permit widespread screening of live animals carrying the infectious agent; the potential weaknesses in the implementation of the preventive measures to control BSE; the risks of microbiological handling due to the increased handling involved, the various origins of cattle; and the conventional sanitization procedures used in the abattoirs cause concerns that the new actions taken by the USDA, in addition to the BSE surveillance program, may not be sufficient to completely eliminate the risk of transmission of BSE prions to humans through meat consumption. The finding that the prions can be detected in animals before symptoms appear may have two (2) alarming implications: (1) that these animals might pass the ante-mortem checking, since they have no clinical signs of central nervous system dysfunction, and could escape the post-mortem tests, because not all animals are tested and, therefore, may enter the food chain; (2) instruments and equipment used on those animals in the abattoirs and meat cutting plants could pass on the disease to BSE negative carcasses.
Despite all the assurances of federal officials that U.S. meat is safe, since the specified risk materials are removed from cows before the meat is processed for human consumption and prions have not been found in beef muscle, a number of countries have banned U.S. beef imports ever since the BSE case was announced on Dec. 23, 2003. Public perception has a profound impact on the beef industry—whether based on facts or media driven emotions. Thus, even the perception of a BSE problem could create an economic crisis.
The consumers' loss of confidence in meat and meat products as well as the associated economic loss result from the lack of adequate methods that offer absolute proof of purity (free of specified risk materials tissues) and safety of meat. Kimberlin et al., (1983) found that at least 104-105 units of infectivity were lost by treatment with hypochlorite (chlorine bleach) containing 1,000 ppm available chlorine after a 4-16 hour exposure. They reported that full strength sodium hypochlorite (20,000-50,000 ppm) is effective for the inactivation of prions on surfaces, such as in the pathology laboratories. Although this procedure may be appropriate for the decontamination of laboratory, operating room, or autopsy room surfaces with central nervous system tissue contact from a known or suspected patient, this approach is unacceptably toxic at this concentration for use in food products.
Taylor, (1998) reported that BSE-infected bovine brain and scarpie-infected rodent brain exposed to 1 or 2 M sodium hydroxide for up to 2 hours did not completely inactivate the infectivity of prions, and permitted the survival of up to four logs of infectivity. Brown et al., (1982) reported that autoclaving for one hour at a temperature of at least 121° C. (15 psi) completely sterilizes CJD-infected materials (metal instruments, glassware, microtome knives). But this procedure cannot be applied to fresh meat carcasses to eliminate pathogenic infectious agents because it is very detrimental to the quality and functionality of the final product.
The prior art indicates that research laboratories have devised sanitization techniques, based on autoclaving and chemical disinfectants, which are suitable for their own purposes but not necessarily applicable to abattoir practice.
The committee on Health Care Issues of the American Neurological Society (Rosenberg et al., 1986) reported that boiling, ultraviolet irradiation, ethylene oxide sterilization, ethanol, formalin, beta-propiolactone, detergents, quaternary ammonium compounds, Lysol, alcoholic iodine, acetone, potassium permanganate are ineffective in inactivating the infectivity of prions.
U.S. Patent Application No. 2004 0213750 A1 describes the use of alkaline ethanolic solutions for disinfecting hard surfaces. There is no suggestion of destroying infectious prions in meat or biological tissue.
Therefore, the prior art has recognized the need for safe and cost effective methods, that are not detrimental to the flavor and texture of the final product, to decontaminate fresh meat carcasses that may have been cross-contaminated with tissues from the specified risk materials of BSE positive cattle containing high titers of infectivity, which expose the consumer to the risk of developing vCJD. There is also a need for the decontamination of biological tissues in general outside of the food supply.